1. Field of the Invention
The present invention relates to a magnification viewer system or loupe known to be worn by surgeons and dentists during certain clinical procedures. In particular, the invention relates to a compact, light-weight, comfortable-to-wear magnification viewer, adapted to be carried by spectacles forming a magnification viewer system. The magnification viewer system provides a relatively wide field of view and good image quality, which minimizes the criticality of the interpupillary distance which, in turn, simplifies adjustment and minimizes reworking of the magnification viewer system.
2. Description of the Prior Art
Magnification viewers are worn by dentists and surgeons for extended periods of time during clinical procedures to provide clarity of view while to avoid a "hunched over" position that can result in debilitating neck and back strain, which can have an adverse effect on the success of the operation. Higher magnification viewers permit the clinician to operate at a greater working distance from the patient. Because clinicians use magnification viewers during surgery and other procedures that require precision, it is important that the viewers be light-weight and comfortable to wear while providing good clarity and a relatively wide field of vision at a relatively high magnification level.
Prior art magnification viewer systems as shown in FIG. 1 are known to employ a pair of magnification viewers 10 attached to a frame of a pair of spectacles 12 by way of a binocular frame 11. The binocular frame 11 provides added weight and complexity to the magnification viewer system, thereby increasing the strain and discomfort to the wearer.
Magnification viewer systems are also known which do not use a binocular frame. In such systems, the magnification viewers are carried by spectacle lenses. One at such viewer is disclosed in Feinbloom, U.S. Pat. No. 3,273,456 ("the '456 patent"). Other systems which involve drilling a hole through a spectacle lens, such as Feinbloom, U.S. Pat. No. 4,364,645; Feinbloom, U.S. Pat. No. 4,555,164; Feinbloom, et al., U.S. Pat. No. 4,863,468; Feinbloom, U.S. Pat. No. 5,129,717; and Feinbloom, U.S. Pat. No. 5,291,229. However, in such magnification viewer systems, the interpupillary distances for the eyepieces are known to be relatively critical, resulting in relatively difficult alignment of the optical system and a significant amount of rework. As such, relatively complicated systems have been developed, such as disclosed in U.S. Pat. Nos. 4,364,645 and 5,090,796, which involve irregularly shaped apertures in the spectacle lenses to which the viewers are inserted to allow for adjustment of the interpupillary distance. Such systems are relatively more complicated and also more expensive.
Known magnification viewer systems are also known to be made according to the Galilean telescope design having a single objective lens and a single eyepiece lens. Galilean telescopes are characterized by relatively narrow fields of view, mainly limited by the diameter of the objective lens. However, the basic Galilean design is known to produce substantial chromatic aberration ("coloring") and hence poor image quality.
It is known that the magnification, or power, of a Galilean design is proportional to the focal length of the objective lens and inversely proportional to the focal length of the eyepiece lens. Thus, the overall viewer length is proportional to the sum of the focal lengths of the objective and eyepiece. Since the dimensions of the viewer should be kept as short as possible to reduce torque on the nose in order to minimize wearer discomfort, an eyepiece with a shorter focal length is usually employed when an increase in magnification is desired. However, in order to retain a good field of view without vignetting, the diameter of the objective lens must be increased. If the diameter of the objective lens is kept the same while keeping the focal length of the objective the same, the "speed" of the lens increases, which results in a lower resolution quality as well as a relatively larger package. One method of overcoming the "speed" problem is to use a more complicated objective lens, which increases the weight and thus strain and discomfort to the wearer, as well as complicating the manufacturing of such a viewer, which increases its cost.
The so-called Kellner design (disclosed in U.S. Pat. No. 1,197,742), known to be used for such magnification viewer systems, contains a relatively heavy doublet or two-piece objective lens and a single eyepiece lens. While the image quality is adequate at lower magnifications, at higher magnifications, excessive coloring results in poor image quality. Moreover, the field of view is relatively limited.
Magnification viewer systems are also known to employ asymmetrical eyepiece lenses having differing radii of curvature on each side lens to ensure that the eyepiece is inserted with the appropriate surface facing outwardly. Such a configuration results in a relatively more complex manufacturing process and relatively high manufacturing costs.